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Nitrogen Availability and Uptake from Field Soils Five Years after Addition of Sewage Sludge¹

ABSTRACT

Nitrogen availability and uptake from sewage sludge were studied in a field experiment during 1979 on a Hubbard sandy loam soil (Entic Haploboroll). Treatments of anaerobically digested (low, 6370; medium, 12 770; and high, 25 200 kg N ha^–1), aerobically digested (12 540 kg N ha^–1) and waste-activated (24 500 kg N ha^–1) sludge were applied between 1972 and 1974. By 1975, 50% more total N remained in plots receiving anaerobic sludge than in plots receiving equivalent N rates of waste-activated or aerobic sludge. By 1979, only 12% of the 1975 level of potentially mineralizable N (N₀) remained in the waste-activated sludge plots, followed by anaerobic sludge (3, 11, and 9% in the low, medium, and high levels, respectively) and aerobic sludge (2%). In 1979, N uptake by maize (Zea mays L.) ranged from 67 kg N ha^–1 to 184 kg N ha^–1 on sludge-treated plots and was 158 kg N ha^–1 on fertilized controls [250 kg N ha^–1 as (NH₄)₂SO₄; 0 sludge]. Due to early depletion of N₀ in aerobic sludge and slow current rate of mineralization of N₀ in waste-activated sludge, N uptake in 1979 from those sludge treatments was 51 and 58%, respectively, as high as from equivalent N application rates of anaerobic sludge. Maize grain and fodder yields reflected the uptake differences. In the 0- to 15-cm soil depth, mineral N at planting time ranged from 23 kg N ha^–1 in aerobic and low anaerobic treatment plots to 31 kg N ha^–1 in medium and high anaerobic treatment plots. Multiple regression analysis indicated the effect of residual mineral N at planting time was more important than N mineralized during the season for both amount and efficiency of N uptake. Low residual NO₃^–-N in the 0- to 15-cm depth limited maize uptake of N mineralized during the season and of previously mineralized N present below the 45-cm depth. The relative influence of residual mineral N on N uptake changed after sludge application. Therefore, combined N indexes and decay series should be used when estimating long-term N supplying power of high sludge applications.

Key Words: aerobically digested sludge • anaerobically digested sludge • corn • N mineralization • residual mineral N • waste-activated sludge

¹ Contribution of the Soil and Water Management Research Unit, North Central Region, USDA-ARS, St. Paul, MN 55108, in cooperation with the Minnesota Agric. Exp. Stn., Sci. J. Ser. Paper no. 13780. Financial support of this research came in part from the Metropolitan Waste Control Commission, St. Paul, MN.

² Research assistant, Dep. of Agron., Kansas State Univ., Manhattan, KS 66506, formerly research assistant, Dep. of Soil Sci., Univ. of Minnesota; research chemist, USDA-ARS, St. Paul, and professor, Dep. of Soil Sci., Univ. of Minnesota; and professor and head, Dep. of Soil Sci., Univ. of Minnesota, respectively.

Received for publication February 3, 1984.